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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - FMA not generated with -ffp-contract=on"
href="http://llvm.org/bugs/show_bug.cgi?id=17211">17211</a>
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</tr>
<tr>
<th>Summary</th>
<td>FMA not generated with -ffp-contract=on
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Driver
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>kkhoo@perfwizard.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>With the following code, I expected to see a "vfmadd*" instruction generated.
I'm not sure what functional differences are enabled by the fp-contract
parameter. It appears to accept "off", "on", and "fast". If I use "fast", I get
the expected codegen.
$ ./clang -v
clang version 3.4 (trunk 189776)
Target: x86_64-apple-darwin11.4.2
Thread model: posix
$ cat fma.c
double foo(double x) {
return x*x + x;
}
$ ./clang -S -O3 -ffp-contract=on -march=core-avx2 -o /dev/stdout fma.c
.section __TEXT,__text,regular,pure_instructions
.globl _foo
.align 4, 0x90
_foo: ## @foo
.cfi_startproc
## BB#0: ## %entry
pushq %rbp
Ltmp2:
.cfi_def_cfa_offset 16
Ltmp3:
.cfi_offset %rbp, -16
movq %rsp, %rbp
Ltmp4:
.cfi_def_cfa_register %rbp
vmulsd %xmm0, %xmm0, %xmm1
vaddsd %xmm0, %xmm1, %xmm0
popq %rbp
ret
.cfi_endproc</pre>
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